Hackers based in Iran have been using malware to spy on individuals, including potentially dissidents and activists in the country, according to new research from Symantec.

The attacks aren't particularly sophisticated, but the hackers have had access to their targets' computers for more than a year, Symantec said, which means they may have gained access to "an enormous amount of sensitive information."

Two groups of hackers, named Cadelle and Chafer, distributed malware that steals information from PCs and servers, including from airlines and telcos in the region, Symantec said.

The groups have been operating since at least mid-2014, but Symantec said registration details for command-and-control servers indicate they may have been running since 2011.

Cadelle uses a piece of malware called backdoor.cadellespy, and Chafer uses one that Symantec calls backdoor.remexi.

It's unclear how Cadelle distributes the malware, but there's evidence that Chafer uses SQL injection attacks to compromise web servers. Such an attack can allow a hacker to enter commands in a Web-based form and get the back-end database to respond.

Each group is thought to be comprised of five to 10 people, according to Symantec. Although they don't share the same attack infrastructure, both are interested in the same targets in Iran and have roughly the same working hours.

An analysis of Cadelspy's file strings revealed that some dates use the Solar Hijri calendar format, common in Iran and Afghanistan.

Some computers were infected with both Cadelyspy and Remexi, with the infections occurring within minutes of one another.

"One computer that was infected with both Cadelspy and Remexi was a system that ran a SIM card editing application," Symantec wrote. "Other compromised computers included those belonging to web developers or are file and database servers."

Another target appears to be people using anonymous proxies -- services that help mask the service a person is connecting to to evade blocks on certain websites.

"Reports have shown that many Iranians avail of these services to access sites that are blocked by the government's Internet censorship," Symantec wrote. "Dissidents, activists, and researchers in the region may use these proxies in an attempt to keep their online activities private."